Frequency dynamics of a chain of magnetized rotors: dumbbell model vs Landau-Lifshitz equation

During the past decades magnetic materials and structures that span several length scales have been of interest mainly due to their application in data storage and processing, flexible electronics, medicine, between others. From a microscopic point of view, these systems are typically studied using the Landau-Lifshitz equation (LLE), while approaches such as the dumbbell model are used to study macroscopic magnetic structures. In this work we use both the LLE and the dumbbell model to study spin chains of various lengths under the effect of a time dependent-magnetic field, allowing us to compare qualitatively the results obtained by both approaches. This has allowed us to identify and describe in detail several frequency modes that appear, with additional modes arising as the chain length increases. Moreover, we find that high frequency modes tend to be absorbed by lower frequency ones as the amplitude of the field increases. The results obtained in this work are of interest not only to better understand the behavior of the macroscopic spins chains, but also expands the available tools for qualitative studies of both macroscopic and microscopic versions of the studied system, or more complex structures such as junctions or lattices. This would allow to study the qualitative behavior of microscopic systems (e.g. nanoparticles) using macroscopic arrays of magnets, and vice versa.

[Traction folliculitis: 6 cases caused by different types of hairstyle that pull on the hair]

Excessive hair traction caused by hairstyles that pull the hair too tightly may cause noninfectious mechanical and irritant folliculitis known as traction folliculitis. We present a series of 6 cases of traction folliculitis caused by different hairstyles. All patients were women aged between 12 and 26 years old. Their hairstyles were braids, ponytails, pigtails, cornrows, and hair extensions in 2 patients. The lesions consisted of small, slightly painful, follicular pustules confined to the sites of maximum hair traction and surrounded by erythema. Only in 1 case were the lesions associated with traction alopecia. In 2 cases in which bacterial cultures were done, Staphylococcus aureus was isolated. All patients improved after undoing their hairstyle and treatment with oral flucloxacillin. We assume that the role of S aureus is secondary and opportunistic, given that only follicles subject to traction and not the adjacent ones were affected.

Circumscribed palmar hypokeratosis: clinical evolution and ultrastructural study after prolonged treatment with topical calcipotriol

Circumscribed palmar hypokeratosis is a recently described condition that consists of a solitary area of depressed skin affecting the palm (or sole). Its histopathological features include a thinned horny layer, a slightly diminished granular cell layer, and intraepidermal vacuolated cells. Prolonged treatment with topical calcipotriol resulted in complete recovery of the affected zone in the case reported here. A second biopsy of the lesion taken at around the fourth year of therapy showed a normalization of the granular layer, a reduction in the intraepidermal vacuolated cells, and a somewhat thicker horny layer. An ultrastructural study carried out at the same time showed a reduction in keratin bundles and keratohyalin granules, and an increase in lipid droplets up to the horny layer. These findings and the therapeutic response to topical calcipotriol support the concept that circumscribed palmar hypokeratosis is a focalized abnormal keratinization defect morphologically expressed at the granular and horny layers.

Structural elucidation of the O-antigenic polysaccharides from Escherichia coli O21 and the enteroaggregative Escherichia coli strain 105

The structure of the O-antigen polysaccharide of the lipopolysaccharide from an enteroaggregative Escherichia coli (strain 105) has been elucidated, using primarily one-dimensional and two-dimensional NMR experiments. The sequence of residues was deduced with heteronuclear multiple-bond correlation and NOESY experiments. The structure of the repeating unit of the polysaccharide from the enteroaggregative E. coli is as follows:[sequence: see text] The structure of the O-antigen from enteroaggregative E. coli strain 105 was shown to be identical with that of E. coli O21 by sugar and methylation analyses as well as by 1H-NMR and 13C-NMR spectroscopy.

Structure elucidation of the O-antigenic polysaccharide from the enteroaggregative Escherichia coli strain 62D1

The O-antigen polysaccharide of the lipopolysaccharide from the enteroaggregative Escherichia coli strain 62D1 has been determined. Sugar and methylation analysis together with 1H and 13C NMR spectroscopy revealed the components of the repeating unit. Two-dimensional NOESY and heteronuclear multiple-bond correlation experiments were used to deduce the sequence. 1H and 13C NMR spectra indicate heterogeneity in the polysaccharide. Methylation analysis and 1H NMR spectra of native and Smith-degraded material show that the majority (65%) of the repeating units has the following structure: Minor resonances in the NMR spectra are consistent with the presence of repeating units which lack the alpha-d-Galp terminal residue (35%).

Structure determination of the O-antigenic polysaccharide from the enterotoxigenic Escherichia coli (ETEC) O101

The O-antigenic polysaccharide of the lipopolysaccharide from the enterotoxigenic Escherichia coli O101 has been investigated. The composition and sequence of the repeating units was established by sugar and methylation analysis together with 1H and 13C NMR spectroscopy. The sequence was corroborated using the computer program CASPER. The structure of the repeating unit of the polysaccharide from E. coli O101 is as follows: -->6)-alpha-D-GlcpNAc-1-->4-alpha-D-GalpNAc-(1-->.

Structural analysis of the O-antigenic polysaccharide from the enteropathogenic Escherichia coli O125

The structure of the polysaccharide part of the lipopolysaccharide obtained from the enteropathogenic Escherichia coli O125 has been investigated. Methylation analysis, 1H-NMR spectroscopy and 13C-NMR spectroscopy revealed that the polysaccharide is composed of repeating hexasaccharide units. Smith degradation of the native O-polysaccharide resulted in a polysaccharide with four sugar residues in the repeating unit. Information on the sequence of the native O-polysaccharide and the Smith-degraded product was obtained by two-dimensional techniques, namely heteronuclear-multiple-bond-connectivity and NOESY experiments. The structure of the repeating unit of the O-polysaccharide of E. coli strain O125, which has two adjacent branch-point residues, is [sequence: see text].

Mal de Meleda

A case of mal de Meleda originating in Chile is reported. The patient had no history of consanguinity and cases could not be detected in four generations of the patient's family. The palmoplantar keratoderma was progrediens and transgrediens, with distant hyperkeratotic plaques of the knees and elbows. The nails, hair, and teeth were normal.

Pigmented follicular cyst

A pigmented follicular cyst is an infrequent variant of an epithelial cyst which has rarely been reported since it was first described about 10 years ago. The condition consists of a single pigmented lesion which occurs predominantly in adult men, and is usually located on the head and neck region. We report an example of a pigmented follicular cyst, which was located in the axilla.

Nevus elasticus and lichen sclerosus et atrophicus on the vulva

A sixty-seven-year-old woman had complained of vulvar pruritus and vaginal soreness for eight months. Clinical and histologic examination showed an admixture of two different entities: nevus elasticus and lichen sclerosus et atrophicus.

Malignant cutaneous mixed tumor. A new case with unusual clinical features

We report the case of an ulcerated malignant cutaneous mixed tumor occurring on the nose of a 75-year-old woman. Malignant cutaneous mixed tumor (CMT) is a rare neoplasm. Of the 14 previously reported cases, 10 occurred on the extremities, three on the trunk, and one on the scalp. This contrasts with the benign CMT which is found mainly on the head and neck region, the nose being the most commonly affected site. Although eight of the cases of malignant CMT recurred and 10 metastasized, the primary lesion never ulcerated.

Self-inflicted tongue ulcer: an unusual form of factitious disorder

Factitious disorders in the buccal cavity are infrequent. A 9-year-old boy with a 5-year history of an artefact ulcer of the tongue is described. Psychiatric evaluation revealed an altered personality structure with a background of psychotic traits. Complete remission was observed with psychiatric management.